This invention relates generally to contrast-based dynamic range management (C-DRM), and more particularly to a method, a related memory medium, and an apparatus for implementing and performing a contrast-based dynamic range management algorithm.
Digital x-ray imaging is a well-known, non-contact technique for observing, in real time, interior aspects of an object. In practice, an x-ray beam is generated and targeted on an object of interest. A detecting device is positioned on the other side of the object and detects the x-rays transmitted through the object. The detected x-ray signals are converted to digital signals that represent various features in the object, are further processed, and the resulting signal is displayed on an image display device such as a CRT.
One of the fundamental image processing problems in digital x-ray imaging is the need to transform the intensity dynamic range of the input image to the dynamic range supported by an available display device. Typically, the intensity dynamic range of an image exceeds the dynamic range of the display mechanism by several times. The objective of the transformation accordingly is to compress the “DC” or mean component of the different regions comprising the image so that the dynamic range (typically 256 gray levels) of an available display device may be utilized in a fashion which maximizes the displayed image contrast taking into account, as well, the generally recognized limitation of the human eye of discerning only 256 gray levels.
Common approaches to achieving such transformations are known as “unsharp masking” and “extended dynamic range (EDR)”, the latter a special adaptation of the former. The conventional approach to performing the EDR algorithm, in general, is simply to subtract a portion of the mean from the input signal. However, if the input image is square root encoded, a contrast gain can be added to compensate to some extent for the non-linear attenuation of the contrast signal and subsequent contrast deficit.